1. Field of Invention
The present invention relates to apparatus for diluting gases, and more particularly, for diluting oxygen with air.
2. Description of Prior Art
Many prior art devices are provided for diluting the concentration of oxygen supplied to patients receiving inhalation therapy. These devices comprise generally a nozzle for securing an oxygen supply tube and a venturi portion into which oxygen is directed from the nozzle. The venturi portion is coupled to atmospheric air for mixing air with the oxygen for diluting the concentration of oxygen. The supply of oxygen may be received generally from a pressurized tank or container of oxygen and in hospitals is usually received from a pressurized hospital supply system. An oxygen mask or other appliance is connected to the mixing chamber of the dilution device by a suitable conduit for delivering the diluted oxygen to the patient.
In the operation of this type of device the flow of oxygen passing from the nozzle through the venturi creates a partial vacuum in the vicinity of the oxygen stream which draws or entrains surrounding atmospheric air which is in fluid communication with the stream into the chamber. Such dilution devices are arranged to provide a single oxygen dilution ratio at a particular oxygen flow rate. The problem with this arrangement is that a separate dilution device is required for each dilution ratio specified for a given patient. Even a large number of such devices with different dilution ratios does not always satisfy medical requirements in that many patients, particularly patients with respiratory disease, have oxygen requirements which may fall somewhere in between the discreet ratios available in conventional single ratio mixing devices. An additional disadvantage of such systems is that it is costly for a user to keep on hand the quantity of dilution devices required including each dilution ratio. Necessarily each dilution device must be disconnected and reconnected in accordance with the requirements of a given patient and is thus cumbersome to implement.
To overcome some of these problems some prior art devices provide an apparatus wherein the atmospheric air inlet port is providied with a variety of aperture magnitudes thus permitting a variety of differing air volumes to be drawn into the mixing chamber by the venturi action. These devices, however, provide for selected air receiving port aperture magnitudes in discreet steps thus limiting the dilution concentration to one corresponding to the selected aperture. These devices are also limited to the range of oxygen concentrations provided. In normal usage it is desirable to provide different oxygen concentrations anywhere within the range of 24% to 100% oxygen. Even those devices with variable air inlet ports do not meet this range of concentration, in addition to being limited to discreet concentration levels. As a result a plurality of even these type of devices may be required by a user and even then not completely fulfill the medical requirements in a particular application. A further discussion of inhalation therapy devices may be found in the text Fundamentals of Inhalation Therapy by Donald F. Egan, C. V. Mosby Co., St. Louis, 1969.